1. Field of the Invention
The present invention relates to double-deficient non-human animals, in which CD9 gene and CD81 gene are deficient, that can be utilized as a model animal for development of therapeutic agents for osteoporosis or therapeutic agents for chronic obstructive pulmonary disease, etc.
2. Description of the Related Art
CD9 and CD81 are known as family members of protein called “tetraspanin”. Tetraspanin is a superfamily, which, as shown by its name, has a structure spanning the cell membrane four times. Until now, about 30 members are known in mammals. Although the tetraspanin is considered to be related to proliferation, movement, and fusion of cells and infiltration and spread of cancer cells, etc., the detail of its function had been unknown. Recently, however, CD81 knockout mice (e.g. Maecker H T. J Exp Med 185:1505-1510, 1997) and CD9 knockout mice (e.g. Miyado K. Science 287:321-324, 2000) were generated and showed abnormal antibody production and cytokine secretion, and infertility, respectively. Therefore, importance of tetraspanin in immune system and in genital system was revealed.
Osteoporosis is a disease, which mainly affects postmenopausal women and elderly people and causes pathological fracture and vertebral curvature. Therefore, there has been a demand for developing a more efficient therapeutic agent for osteoporosis, but there are not many experimental animal models for osteoporosis. At present, as an osteoporosis model animal, an ovariectomized mouse is often used, and this mouse is considered to be suitable as a model animal for osteoporosis with increased osteoclast activity due to reduced estrogen, which is common in postmenopausal women. On the other hand, as a mechanism of osteoporosis, so-called low-turnover type is also known in which the bone formation activity of osteoblasts is reduced, and a model animal that exhibits such low-turn over type is sought.
The relationship between osteogenesis by osteoblast and the tetraspanin had not been known at all.
Chronic Obstructive Pulmonary Disease (hereinafter may be referred to as “COPD”), which is an obstructive respiratory functional impairment, is comprised of two diseases: lung emphysema characterized by destruction of alveolar walls and enlargement of air spaces; and chronic bronchitis which involves persistent increase of respiratory secretions, and these two diseases often coexist. Its pathophysiology is abnormal inflammatory cell infiltration into the lung and production of proteolytic enzyme as a result of smoking.
Smoking is a major risk factor for COPD and the morbidity rate is increasing around the world. According to WHO, COPD is the fifth commonest cause of death at present and it is anticipated that it will be the third in 2020. However, its pathogenesis is still unclear. Only 15% to 20% of smokers develop COPD, and it is thought that sensitivity to smoking vary between individuals; however, there is not enough scientific support to demonstrate it.
Recently, it has been increasingly recognized that COPD patients not only have lung disease, but also frequently develop weight loss and muscle weakness and systemic complications such as osteoporosis, which accelerates the reduction of ADL and respiratory function (e.g. Biskobing D M. Chest 121:609-620, 2002). Administration of steroid drug, vitamin D deficiency, smoking, etc. are considered to be causes of these systemic changes, but mechanisms of these extrapulmonary effects are unknown.
Several genetically engineered mice have been produced in order to elucidate mechanisms of lung emphysema and to develop novel treatment strategies. For example, mice overexpressing the collagenase, one of proteinases, develop lung emphysema. Regarding knockout mice, models for lung emphysema are not many, although it is reported that mice such as surfactant protein D knockout and integrinβ knockout mice develop emphysema. (e.g. Wert S E. Proc Natl Acad Sci USA 97:5922-5977, 2000 and Morris D G Nature 422:169-173, 2003). Furthermore, these mice were not reported to develop extrapulmonary effects such as osteoporosis in addition to lung emphysema.